1. Field of the Invention
The present invention relates to hand held data collector and analyzer devices and particularly to devices capable of collecting and analyzing vibration and/or ultrasonic data.
2. Background and Description of the Related Art
Hand held data collector and analyzer devices are generally used to collect vibration or ultrasonic data from machines or systems for use in predicting maintenance applications. Such data collectors and analyzers may be programmed to be loaded with a route from a central computer, and such route may include a list of machines, test points, and a set-up conditions for each test point. Typical routes comprise dozens of machines or systems to be checked in the route with dozens of test points on each machine or system, and for each test point there may be specified a frequency range to be analyzed, a type of analysis to be performed, a particular type or set of data to be stored, and similar other parameters. Based on inputs from the user, the hand held instrument prompts the user as to the identity of the machine and the test point to be monitored, and it automatically sets up the instrument, for example, to record a predetermined frequency range for the test point, conduct a predetermined analysis and store a predetermined set of data. Data are thus collected along the route and then transferred to the central computer for storage and subsequent treatment.
These hand held devices are in industrial environments exposed to a large range of vibrations, temperatures, pressures etc. . . . and must however remain capable of monitoring vibration or ultrasonic sources accurately in those conditions.
For example, to distinguish a click associated with a crack in a bearing, a user will usually select a frequency range of interest and look for a specific frequency that may indicate a cracked bearing.
Typical known data collector and analyzer devices use an analog signal processing unit comprising an analog filter element to remove some of the unwanted frequency components and then shift the signal frequency range in an appropriate bandwidth, such as in the audible frequencies. Such a filter element usually comprises a mixer element arranged for mixing the amplified analog signal with a square wave signal and a filtering element receiving the mixed signal and removing the unwanted portion of this signal, these mixing and filtering operations leading to the above shifting of the signal frequency range. One approach to achieve the frequency analysis capability has been to introduce in the analog signal processing unit a programmable analog low-pass filter (LPF) whose cutoff frequency can be controlled for selecting the frequency range that needs to be analysed. The output of the filter is then sampled by an analog-digital converter (ADC) to provide a digital signal that is operated on by a digital signal processing unit.
Such devices do however suffers from inconveniencies. Namely, programmable analog low-pass filters such as anti-aliasing filters, will produce a certain amount of distortion of amplitude, frequency and phase that may be critical in certain applications.
Limitations at the higher end of the frequency range appear in such prior art devices but some instruments are also unstable at low frequencies. This characteristic usually results from circuit designs focused on certain preferred frequency ranges because such frequencies are generally of greater interest.
On the other hand, digital programmable low-pass filters can be rendered much more stable.
An example of devices comprising programmable analog low-pass filters is described in U.S. Pat. No. 6,189,384, which relates to a route-base ultrasonic monitoring device, capable of collecting and analysing signals in the ultrasonic bandwidth and possibly also temperature (infra-red) signals.
It has been proposed to overcome the above problems of distortion of the signal arising with analog filters by providing hand held data collectors and analyzers with a digital signal processing unit comprising digital filters instead of their analog counterparts for filtering the signal after it has been digitalised, ie sampled, by the convertor. On the other hand, digital low pass filters enable a very low level of distortion of the signal and are much more easy to parameterise since this is achieved by way of a software instead of hardware components. An example of a collecting and analysing hand held device of this kind is described by U.S. Pat. No. 5,870,699. The described device however is solely capable of collecting and analysing signals in the vibration bandwidth. Another more recent prior art device solely capable of collecting and analyzing signals in the vibration bandwidth is described in U.S. patent application no. 2005/0060123.
Prior art devices thus do not combine digital shifting and possibility of collecting and analysing signals in both the ultrasonic and vibration bandwidths.